Abstract
Psychological stress and occlusal alteration are important etiologic factors for temporomandibular/masticatory muscular disorders. In particular, the exact physiologic mechanism underlying the relation by occlusal alteration and temporomandibular disorders remains unclear. Our purpose was to test the hypothesis that benzodiazepine therapy is able to prevent metabolic and vascular changes in the medial pterygoid muscle of rats under chronic stress after 14 days of unilateral exodontia. Adult Wistar rats were submitted to unpredictable chronic mild stress (10 days) and/or unilateral exodontia and their plasma and medial pterygoid muscles were removed for analysis. A pre-treatment with diazepam was used to verify its effect on stress. The parameters evaluated included anxiety behavior, plasma levels of corticosterone, metabolic activity by succinate dehydrogenase, capillary density by laminin staining and ultrastructural findings by transmission electron microscopy. Occlusal instability induced anxiety-like behavior on elevated plus-maze test and diazepam administration blocked the appearance of this behavior. Unilateral exodontia promoted in the contralateral muscle an increase of oxidative fibers and capillaries and modification of sarcoplasmic reticulum. Chronic stress caused increased glycolytic metabolism, reduced capillary density and morphological changes in mitochondria on both sides. Association of both factors induced a glycolytic pattern in muscle and hemodynamic changes. Pharmacological manipulation with diazepam inhibited the changes in the medial pterygoid muscle after stress. Our results reveal a preventive benzodiazepine treatment for stress and occlusal instability conditions affecting masticatory muscle disorders. In addition, provide insights into the mechanisms by which chronic stress and exodontia might be involved in the pathophysiology of masticatory muscular dysfunctions.
Highlights
Psychological stress and occlusal alteration are important etiologic factors for temporomandibular/ masticatory muscular disorders
This study hypothesizes that unpredictable chronic mild stress influences on morphophysiological changes in the right and left medial pterygoid muscle (MPM) induced by occlusal instability (Fig. 1) and that classic pharmacological manipulation with benzodiazepine reverses the alterations caused, since diazepam shows anti-stressor and anxiolytic-like activities
Considering the percentage of time spent in open arms, the application of a two-way ANOVA showed a significant decrease (Newman Keuls test) in time spent by rats that underwent molar exodontia and/or stress treated with vehicle compared to that one treated with diazepam (P < 0.05; Fig. 2B)
Summary
Psychological stress and occlusal alteration are important etiologic factors for temporomandibular/ masticatory muscular disorders. Association between emotional stress and occlusal instability, in case of orthodontic treatment, masticatory disorders and the removal of third molars, have been involved with the development of temporomandibular joint disorders and maintenance of pain[3]. The influence of occlusal alteration in the MPM of gerbils, previously described by Iyomasa et al.[7], shows muscle fibers with a central nucleus and decreased diameter six days after unilateral exodontia It has been admitted, that dysfunctional occlusion can affect morphology and function of masticatory muscles[8,9]. This study hypothesizes that unpredictable chronic mild stress influences on morphophysiological changes in the right and left MPMs induced by occlusal instability (Fig. 1) and that classic pharmacological manipulation with benzodiazepine reverses the alterations caused, since diazepam shows anti-stressor and anxiolytic-like activities.
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